1. Field of the Invention
The present invention relates to a photoconductor for electrophotography to be used for forming images by an electrophotographic process such as a copying machine, a printer, a facsimile, etc., and a method of manufacturing the photoconductor.
2. Description of Related Art
In an image forming system using an electrophotographic photoconductor, after electrically charging the surface of the photoconductor having a photo conductivity by means of corona discharging or the like, an electrostatic latent image is formed thereon by image exposure, and finally a visual image is developed with toner.
What becomes a problem in the electrophotographic photoconductor used in this system is a local charging failure due to a defect of the photoconductor, and this results in an extremely poor image such as a black point or a fog in the image. Various factors can be considered as causes for an occurrence of such a local charging failure, and most of the failures are considered to occur due to a local charge injection between a conductive supporter and a photoconductive layer.
Most of the conductive supporters use aluminum or an alloy including aluminum as a main component for a substrate, and a blocking layer is provided between the aluminum substrate and a photoconductive layer to prevent an occurrence of the problem. As known techniques, there have been methods for providing resin layers of polyamide, polyimide, polyvinylalcohol, polyurethane, casein, cellulose, etc. and inorganic layers of aluminum oxide, aluminum hydroxide, etc. A method of providing an inorganic layer, or an anodic oxidation (or anodized) layer, as a blocking layer is used with a view to improving a close adhesion of a photoconductive layer and facilitating the cleaning as well as preventing a reduction in the drop of a charged level.
Further, in recent years, organic materials have been widely used for photoconductive layers. This is because organic materials have such advantages as their low materials costs, low manufacturing costs and no environmental problems involved. These organic materials are coated in points or coatings on an anodic oxidation layer by a dip coating method and a ring coating method. In order to form a uniform and stable photoconductive layer, it is necessary that the coating has both excellent dispersiveness and solubility. In order to meet this requirement, various kinds of solvents have been used in the coatings, and particularly, the use of a high boiling-point solvent has been investigated. When a high boiling-point solvent is used, a drying process at high temperature is naturally required in order to eliminate solvent components by evaporation.
However, even if an electrophotography photoconductor having the above-described blocking layer is used, it is difficult to achieve an improvement of completely eliminating the image defects such as back points and fog. Particularly, the occurrence of a fog is extreme under the environment of high temperature and high humidity.
Further, an anodic oxidation layer is gradually oxidized naturally and its heat-resisting property is deteriorated along with the lapse of time. When the heat-resisting property is deteriorated, various problems, such as cracks occur on the surface of the layer during a drying process, uneven coating at the time of forming a photoconductive layer, dielectric breakdown strength is lowered, cracks occur increasingly in the photoconductive layer, etc.
Moreover, because of a porous surface state of the anodic oxidation layer, a contamination in the air once adsorbed on this surface is difficult to be removed. Even if the layer is tried to be cleaned with a liquid such as an organic solvent or the like, the liquid cannot be removed completely after the cleaning, with a fine quantity of the liquid remaining on the layer as a result. The cleaning of the anodic oxidation layer with a liquid solvent results in a rapidly progressive oxidation of the layer surface, which further increases the possibility of occurrence of cracks on the layer.
Further, in Japanese Patent Application Examined Publication No. 7-120062, there is disclosed an electrophotography photoconductor having an anodic oxidation layer which has been seal processed and which has a product of Ym.times.d as not more than 4.times.10.sup.-10 (S.m), where d represents an average layer thickness of the anodic oxidation layer and Ym represents admittance, in order to solve the problems of black points and fogging.